The Organic Light Emitting Display (OLED) possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED can be categorized into two major types according to the driving methods, which are the Passive Matrix OLED (PMOLED) and the Active Matrix OLED (AMOLED), i.e. two types of the direct addressing and the Thin Film Transistor (TFT) matrix addressing. The AMOLED comprises pixels arranged in array and belongs to active display type, which has high lighting efficiency and is generally utilized for the large scale display devices of high resolution. The AMOLED is a current driving element. When the electrical current flows through the organic light emitting diode, the organic light emitting diode emits light, and the brightness is determined according to the current flowing through the organic light emitting diode itself. In the AMOLED driving circuit, the threshold voltage of the drive thin film transistor will drift along with the working times. Thus, it results in that the luminescence of the OLED is unstable. Therefore, the pixel driving circuit which can compensate the drift of the threshold voltage of the drive thin film transistor is required to be utilized.
FIG. 1 shows an AMOLED pixel driving circuit according to prior art, comprising a second switch thin film transistor SW2, and a gate thereof is electrically coupled to an nth second scan control signal gate2(n), and a drain is electrically coupled to a data signal data, and a source is electrically coupled to a source of a mirror thin film transistor MR and one end of the second capacitor Cst2; the mirror thin film transistor MR, and a gate thereof is electrically coupled to a source of a drive thin film transistor DR via a first node D, and a drain is electrically coupled to a drain of a first switch thin film transistor SW1, and the source is electrically coupled to the source of the second switch thin film transistor SW2 and the one end of the second capacitor Cst2; the first switch thin film transistor SW1, and a gate thereof is electrically coupled to an nth first scan control signal gate1(n), and a drain is electrically coupled to the drain of the mirror thin film transistor MR, and a source is electrically coupled to the first node D; a pre-charge thin film transistor PC, and both a gate and a source thereof are electrically coupled to an n−1th second scan control signal Gate2(n−1), and a drain is electrically coupled to the first node D; the drive thin film transistor DR, and a gate thereof is electrically coupled to the gate of the mirror thin film transistor MR via the first node D, and a drain is electrically coupled to the ground GND, and a source is electrically coupled to an cathode of the organic light emitting diode OLED; one end of a first capacitor Cst1 is electrically coupled to the first node D, and the other end is electrically coupled to the ground GND; one end of a second capacitor Cst2 is electrically coupled to the source of the second switch thin film transistor SW2 and the source of the mirror thin film transistor MR, and the other end is electrically coupled to the ground GND; an anode of the organic light emitting diode OLED is electrically coupled to the power supply voltage VDD, and the cathode is electrically coupled to the source of the drive thin film transistor DR. FIG. 2 is a sequence diagram of an AMOLED pixel driving circuit shown in FIG. 1. The compensation procedure of the circuit sequentially comprises a Pre-charge stage, a Program stage, a Restore stage and a Drive stage, wherein in the restore stage, the gate voltages Vg of the drive thin film transistor DR and the mirror thin film transistor MR are equal, and the data signal data is required to be recovered to the ground GND to pull down the source voltage Vs of the mirror thin film transistor MR to make the gate-source voltage of the drive thin film transistor DR and the gate-source voltage of the mirror thin film transistor MR close. Then, both the stresses and the times of the voltages which the drive thin film transistor DR and the mirror thin film transistor MR are suffered are close. The threshold voltage drifts are close, too. Thus, the mirror thin film transistor MR can replace the drive thin film transistor DR to detect the threshold voltage for compensating the influence of the threshold voltage drift of the drive thin film transistor DR to the circuit. As shown in FIG. 3, the AMOLED pixel driving circuit according to prior art uses the way of recovering the data signal to the ground GND to achieve that the stresses of the gate-source voltages of the mirror thin film transistor MR and the drive thin film transistor DR are close. However, such way will shorten the charge time of the data signal Data.